The efficacy of the Merck hepatitis B ayw vaccine will be evaluated in a placebo-controlled, randomized, and double blind trial. Approximately 1000 HBV susceptible patients and 1000 medical personnel from 23-24 large dialysis centers will be acceded. Injections will be given at entry into the trial and one month later with boosters at six and 24 months; pending the results of a pre-trial immunogenicity study, additional boosters may be given to the participating patients. Routine follow-up blood specimens will be taken monthly for a two year period. The results will be evaluated in terms of antibody responses and attack-rates of HBV events in participants treated with the vaccine and placebo. It is anticipated that at least 80% of the vaccinated staff and 65-70% of patients will be protected. Three and one-half years will be required to study efficacy and another one and one-half to fulfill other study objectives.